Spray coating methods of applying fluorine containing dispersions onto substrates such as EPDM and nitrile rubber already exist. They are typically combined with primers such as but not limited to polyamide-imide, polyether sulfones and sprayed onto a substrate that may have been pretreated with methyl-ethyl ketone, N-methyl pyrrolidone, plasma or corona treatment to improve adhesion of the primer to the substrate. Following surface preparation and priming, they are coated with a fluorine containing dispersion coating, and are then cured on-line or off-line in an oven. However such methods have not previously been applied to a diffuser membrane for use in water treatment plants, which is a difficult application.
This improvement is of particular importance in application of such a coating to a diffuser membrane used in the sewage and industrial wastewater treatment industries. Diffuser membranes are typically made from perforated non-fluorinated elastomers or polymers, which are perforated with small slits and, when inflated, produce a plume of bubbles which are released into wastewater. The efficacy of such diffusers is measured primarily in their ability to produce small bubbles in great quantity, such that the combined surface area of the bubbles is large. A large quantity of small bubbles transfers much more oxygen to the process than do a smaller quantity of large bubbles and oxygen mass transfer is desirable. Manufacturers of diffusers typically spend a great deal of time and energy formulating elastomeric compounds that produce small bubbles. The slightest compound formulation change may result in a vastly different bubble size. Furthermore, where diffuser membranes are submerged in dirty water, surface contamination from foulants such as biofilm, calcium and gypsum can cause an increase in bubble size over time, just as fats, oils, greases and solvents can penetrate traditional membranes causing chemical oxidation of the rubber. This can result in either a failed part or increased bubble size. The coating of a non fluorine containing membrane with a smooth fluorinated layer that is specifically designed to produce small bubbles, and to withstand thousands of perforations and a constant state of flux while submerged in wastewater is a novel invention and provides a universal solution to both fouling and efficiency issues.